As is well known in the art, conventional inkjet printers generally employ one or more inkjet cartridges, often called “pens”, which shoot drops of ink onto a page or sheet of print media. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. The pens are usually mounted on a carriage, which is arranged to scan across a scan axis relative to a sheet of print media as the pens print a series of individual drops of ink on the print media. The series of drops collectively form a band or “swath” of an image, such as a picture, chart or text. Between scans, the print medium is advanced relative to the scan axis. In this manner, an image may be incrementally printed.
A continuing goal of inkjet printing technology is to increase the speed (i.e. reduce the time) with which an image may be printed. Various factors limit the speed with which an image may be printed. Amongst these factors is the time that the printhead carriage requires to scan across the print media. This time is especially important in unidirectional print modes, which are usually used to achieve high print quality. In unidirectional print modes, ink is printed only whilst the carriage is moving in one direction along the scan axis. Thus, for every printed swath, a non-printing return movement of the carriage along the scan axis is required.
One known method of avoiding this limitation is to use a page wide array (PWA) of printheads. In PWA printers, an array of printheads extending across the width of the page is used. Thus, ink may be ejected across the entire printable width of the print media, without moving the printheads across the width of the page. Generally, the print medium is then fed in a direction perpendicular to the array of printheads while the array of printheads is maintained stationary. In this manner, such scanning times may be eliminated.
In order to maintain the quality of the printed output of the printer device, it is important that each instruction to the print head to produce an ink drop from a given nozzle does indeed produce such an ink drop. Thus, it is important to verify that each nozzle is functioning correctly.
In order to achieve this, it is common practice in ink jet devices, to periodically initiate a “spitting” routine, whereby a nozzle may be purged by sending it a sequence of fire pulses, possibly of greater energy than the normal firing pulse. This serves to ensure that the ink contained in the nozzles does not dry, causing a blockage of dry ink, which stops the nozzle from firing correctly. Spitting routines also help to clear already blocked, or partially blocked nozzles, which may be caused by paper fibers or dried ink, for example.
Such techniques are used in many conventional inkjet printers, such as the Hewlett-Packard DesignJet 1050 and Hewlett-Packard DesignJet 5000. However, as is conventional in such systems, in order to carry out each spitting routine, the printheads are moved to a service station located away from the print zone of the printer, where the nozzles may spit into a spittoon which is designed to receive and store the ink expelled during the spitting procedure. After the spitting procedure is complete, the printheads are returned to the print zone where they may then continue to print. This process is time consuming and throughout the whole process, the printer is unable to print. Therefore, such techniques are not well suited to PWA systems. This is because, a PWA system may have a very high number of nozzles, tens of thousands for example, that very frequent spitting routines are required. Furthermore, since they aim to provide increased throughput, relative to conventional scanning inkjet printers, they are less tolerant to printing downtime.
It would therefore be desirable to provide an improved system and method for servicing ink jet devices.